1. Field of the Invention
The present invention pertains to the field of artificial limbs for use by individuals who have lost a limb, especially a foot, through injury or amputation. More particularly the invention is directed toward an improved socket of an artificial limb into which the residual limb or amputation stump is mounted.
2. Background Information
Artificial limbs typically include a socket which is used to support and connect the residual limb of a patient to the artificial limb. The residual limb is inserted into the socket and it is therefore desirable that the socket should have a close fit around the residual limb to provide a good connection between the residual limb and the artificial limb with a minimum amount of pressure points on the residual limb. For this reason the sockets are custom made so that they conform to the configuration of the residual limb so as to be capable of supporting weight, in the case of a leg, or loading forces, in the case of an arm.
It has been found that it is highly desirable for patients to begin use of artificial limbs or prosthetic devices as soon as possible after loss of the limb through accident or amputation. If a patient can be fitted with a prosthetic device after limb amputation, the prognosis for long term, effective use of the prosthetic device is much higher. However, it is very difficult to obtain a good fit around the residual limb soon after loss of the limb through amputation or accident. This is because of the substantial edema or swelling which takes place after the loss of the limb regardless of whether the loss of limb is caused by amputation or injury. The edema will continue for about two or three months until sufficient healing has taken place which allows the fluids to be reabsorbed from the area of swelling.
Since limb prosthetic devices are most typically mounted to a patient by a socket which is customized to the configuration of the patient's residual limb, formation of a prosthetic socket within a few weeks of limb amputation results in a socket which conforms to the configuration of the swollen or edema-affected residual limb. However, as the edema or swelling gradually diminishes, the initial close fit will become more loose.
One approach for dealing with the gradual loosening of the fit between the residual limb and the socket has been the addition of increasing layers of socks over the residual limb before placing the residual limb in the socket. The additional socks are used to fill the space left in the socket as a result of decreasing edema.
Another approach is to simply recast the socket after the edema has disappeared. This approach is obviously costly. Still another approach is to wait until the edema has subsided before forming the prosthetic socket. This approach, however, is undesirable because it does not permit the amputee to obtain the therapeutic benefits associated with early use of the prosthetic device.
The above-noted use of socks is also undesirable because the socks change in volume with pressure, which means that the fit of the socket is dependent on the loads applied, hence the actions of the user. Another problem with such socks is loss of control, as multiple plies of socks allow the socket to rotate and move on the residual limb.
Several attempts have been made to manufacture a device that allows the user to control the volume of the socket. These include air bladders and various types of pumping mechanisms. These devices function on a pneumatic principle wherein air is used as a media to change the volume. The main problem with using air is that it is compressible and therefore the same problems occur as with the socks.